The present application is based on and claims priority from Japanese Patent Application 2001-125413, filed Apr. 24, 2001, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a rotary electric machine to be mounted in a passenger car or a truck.
2. Description of the Related Art
The engine compartment of a vehicle has become narrower due to a tendency of vehicle""s nose being slanted in order to reduce vehicle running resistance. Therefore, there is a small space for accessories and parts such as a vehicle AC generator in the engine compartment.
In addition, the idling speed of the engine is lowered to improve fuel consumption, while various devices such as devices for safety are added. Therefore, a demand for a compact and powerful vehicle AC generator that can generate large power at a low speed range has been growing.
In order to increase the output power of the AC generator, a flat or rectangular copper wire is used for the stator winding of the AC generator, so that the ratio of the conductor cross-section to the cross-section of the slot, or the space factor, can be increased.
However, the flat copper wire has sharp corners, where insulation coating may become uneven and very thin. Such insulation coating may be accidentally broken by foreign particles that are kicked up by a vehicle wheel and introduced into the inside of the AC generator.
JP-U-56-17856 discloses a rotary electric machine in which on a side of a copper wire has a round surface while other three sides of the wire have flat surfaces. However, it is practically difficult to provide this type of copper wire in view of manufacturing processes and costs. For example, it is necessary to place the round-surface-side in a fixed position.
Therefore, the present invention has been made in view of the above problems.
It is an object of the invention to provide an improved vehicle rotary electric machine that is equipped with a flat wire having insulation coating that is not damaged by foreign particles.
According to features of the invention, a stator winding is accommodated at a plurality of slots in a plurality of radially extending layers. The stator winding is comprised of a plurality of U-shaped conductor segments having a pair of straight portions disposed in the slots in the layers and a turn joint portion forming coil ends. Those of the straight portions disposed in one of opposite ends of layers have outside corners whose radius is larger than corners of others of the straight portions.
Therefore, the insulation coating can cover the corners evenly and can protect the stator winding from foreign particles or the like effectively. Preferably, the plurality of U-shaped conductor segments comprises large size U-shaped conductor segment group and small size U-shaped conductor segment group. The pair of straight portions of the large size U-shaped conductor segment group is disposed in the opposite radial end layers.
Therefore, only the large size U-shaped conductor segment group of the U-shaped conductor segments has to have outside corners in each slot that correspond to the corners of the slot. Accordingly, it is easy to provide such outside corners. It is also easy to identify the large size U-shaped conductor segment from other segments by the size thereof, thereby preventing errors in the manufacturing process. Since it is not necessary to increase the radius of the corners of the U-shaped conductor segments other than the large size U-shaped conductor segment group, the ratio of the cross-section of the straight portions relative to the space of the slot can be maximized.
According to another feature of the invention, a cooling fan disposed at an end of said rotor. Preferably, a pair of cooling fan may be disposed at opposite ends of the rotor.
Therefore, cooling air driven by the cooling fan can flow around the coil ends smoothly, and the stator winding 23 can be cooled more effectively and fan noises can be reduced.